1. Field of the Invention
The present invention relates to an image input apparatus and method for correctly inputting a reflected light image of an object without the influence of a change of external light such as a fluorescent lamp.
2. Description of the Related Art
In a computer system of the prior art, in order to virtually generate a character model in three-dimensional space, a method for obtaining a distance image is well known, as shown in Japanese Application No. PH9-299648. In this method, first, a light is emitted to an actual object imitative of the character model. Second, light reflected from the object is obtained and an image is generated by the reflected light. In this way, the reflected light image represents the shape of the object. In this case, the reflected light from a far background is very slight. Therefore, the shape of the object is easily separated from the background in the reflected light image. If the object includes a reflected characteristic uniformly, this object reflected light closely represents the three-dimensional shape. Therefore, the object-reflected light is transformed into a three-dimensional image. Furthermore, three-dimensional movement of the object is easily extracted from a series of object-reflected light images. FIG. 1 shows, as one example, the reflected light image of a human's right hand.
In order to extract the reflected light image, the reflected light from the object is only detected without an external light such as an illumination light or sunlight. Therefore, image input operation is executed two times. At one time, a light is emitted to the object. At the other time, the light is not emitted to the object. The difference between the two images inputted at the two times is calculated as the object-reflected light. These two input operations are executed at a very short interval, and the change of quantity of the external lights between the two input operations is small. However, in an illumination environment such as that created by a fluorescent lamp whose intensity is changing, the external light changes at very short intervals between the two input operations. As a result, the quantity of the reflected light image falls because the shape of the object is not correctly represented in the reflected light image.
Furthermore, in illumination such as that created by a fluorescent lamp, the intensity basically changes in proportion to the cycle of the power supply. However, a waveform change is not clear as a sine wave and partially includes an immediate change. In short, the waveform change includes a harmonic. Therefore, in this case, the reflected light image includes the mixture of the shape of the object and the change element of the external light.
Furthermore, if two input operations are simply executed at an interval “10 ms” such as a flickerless operation of a CCD camera, the time difference between the two input operations is long. In this case, if the object is moving quickly, the quality of the reflected light image falls. As for an LED used as an emission source, the shorter the emission time is, the brighter the LED momentarily emits by power. Therefore, if the stored time of the reflected light is long, the ratio of the external light to the reflected light is large and the dynamic range to input the reflected light is narrow.